Search

Tomo-e Gozen (Tomo-e) is a wide field optical camera for the Kiso 1.05 m f/3.1 Schmidt telescope operated by the University of Tokyo. Tomo-e is equipped with 84 chips of front-illuminated CMOS image sensors with a microlens array. The field of view is about 20 square degrees and maximum frame rate is 2 fps. The CMOS sensor has 2160x1200 pixels and a size of pixel is 19 microns, which is larger than those of other CMOS sensors. We have evaluated performances of the CMOS sensors installed in Tomo-e. The readout noise is 2.0 e- in 2 fps operations when an internal amplifier gain is set to 16. The dark current is 0.5 e-/sec/pix at room temperature, 290K, which is lower than a typical sky background flux in Tomo-e observations, 50 e-/sec/pix. The efficiency of the camera system peaks at approximately 0.7 in 500 nm.

We report the initial result of an adaptive-optics assisted, optical integral-field-unit observation on IRAS04576+0912, the nearest (z=0.039) active galactic nucleus with a prominent blueshift/tail in [O III] emission from a sample of such objects that we have collected from the literature. We aim at addressing the putative quasar-mode feedback process with Subaru/Kyoto 3D II+AO188. The optical waveband (6400--7500 AA) enables us to measure the gas density via the [S II] doublets, in contrast to earlier Near-IR studies. Since the fast [O III] outflow happens only around rapidly growing central black holes, this object is suitable for investigating the black hole-galaxy coevolution. The obtained data cube exhibits blue tail in the [S II] emission at many lenslets. By fitting the spectrum with the high excess flux at the [S II] blue tail, we find the fast (~ 860 km/s), dense (>3000/cc), wide-angle and offset outflow in central 100-pc scales. Although the large opening angle and the high gas outflow-to-accretion ratio may favour the feedback hypothesis, the inferred kinetic power injection rate of this ionized gas outflow seems insufficient to influence the whole host galaxy. A conventional assumption of a low density must have overestimated the feedback process., 7 pages, 2 figures, Accepted for publication in PASJ

The Tomo-e Gozen is a wide-field high-speed camera for the Kiso 1.0-m Schmidt telescope, with a field-of-view of 20.7-deg2 covered by 84 chips of 2k x 1k CMOS image sensors with 19-μm pixels. It is capable to take consecutive images at 2-fps in full-frame read with an absolute time accuracy of 0.2 millisecond. The sensors are operated without mechanical coolers owing to a low dark current at room temperature. A low read noise of 2-e- achieves higher sensitivity than that with a CCD sensor in short exposures. Big data of 30-TBytes per night produced in the 2-fps observations is processed in real-time to quickly detect transient events and issue alerts for follow-ups.

We report the discovery of an SN1988Z-like type IIn supernova KISS15s found in a low-mass star-forming galaxy at redshift z=0.038 during the course of the Kiso Supernova Survey (KISS). KISS15s shows long-duration optical continuum and emission line light curves, indicating that KISS15s is powered by a continuous interaction between the expanding ejecta and dense circumstellar medium (CSM). The H$\alpha$ emission line profile can be decomposed into four Gaussians of narrow, intermediate, blue-shifted intermediate, and broad velocity width components, with a full width at half maximum of $\lesssim 100$, $\sim 2,000$, and $\sim 14,000$ km s${}^{-1}$ for the narrow, intermediate, and broad components, respectively. The presence of the blue-shifted intermediate component, of which the line-of-sight velocity relative to the systemic velocity is about $-5,000$ km s${}^{-1}$, suggests that the ejecta-CSM interaction region has an inhomogeneous morphology and anisotropic expansion velocity. We found that KISS15s shows increasing infrared continuum emission, which can be interpreted as hot dust thermal emission of $T \sim 1,200$ K from newly formed dust in a cool, dense shell in the ejecta-CSM interaction region. The progenitor mass-loss rate, inferred from bolometric luminosity, is $\dot{M} \sim 0.4 M_{\odot} \text{yr}^{-1} (v_{w}/40 \text{km}~\text{s}^{-1})$, where $v_{w}$ is the progenitor's stellar wind velocity. This implies that the progenitor of KISS15s was a red supergiant star or a luminous blue variable that had experienced a large mass-loss in the centuries before the explosion., Comment: 43 pages, 29 figures, and 12 tables, accepted for publication in the Astrophysical Journal (ApJ) 2019 January 15

The Kyoto Tridimensional Spectrograph II (Kyoto 3DII) is an optical integral field spectrograph mounted on the Subaru telescope as a PI-type instrument. Used with AO188, Kyoto 3DII provides us unique opportunities of optical Integral Field Spectroscopy (IFS) with adaptive optics (AO). While AO works better in redder wavelength regions, quantum efficiency of the previous CCD was low there with optimization for a wider wavelength coverage. To optimize Kyoto 3DII to AO observations, we have newly installed the red-sensitive Hamamatsu fully depleted CCD, which enhances the system efficiency by a factor of ~2 in the red wavelength range. Fringes are dramatically reduced, and the readout noise drops to 3:2-3:4e- about two times smaller than previous, due to refrigerator and readout system. With these improvements, we carried out engineering and scientific observations in September 2015, February and March 2016. We measured the system efficiency using a standard star, and confirmed the successful improvement of the system efficiency. We observed galactic nuclei of nearby galaxies in the Natural Guide Star (NGS) and the Laser Guide Star (LGS) modes. We found the spatial resolution of ~0.1′′ FWHM using a 9.5-magnitude NGS, and ~0.2 - 0:4′′ in LGS mode. Together with the AO resolution, improved efficiency opens a new window for Kyoto 3DII to carry out high resolution optical IFS targeting faint objects such as high-redshift galaxies as well as faint lines such as [OI] λ6300° A and absorption lines of nearby objects.

The Tomo-e Gozen is an extremely wide-field optical camera for the Kiso 1.0-m Schmidt telescope. It is capable of taking consecutive frames with a field-of-view of 20 deg2 and a sub-second time-resolution, which are achieved by 84 chips of 2k×1k CMOS sensor. This camera adopts unconventional designs including a lightweight structure, a nonvacuumed and naturally-air cooled system, front-side-illuminated CMOS sensors with microlens arrays, a sensor alignment along a spherical focal plane of the telescope, and massive readout electronics. To develop technical components necessary for the Tomo-e Gozen and confirm a feasibility of its basic design, we have developed a prototype-model (PM) of the Tomo-e Gozen prior to the final-model (FM). The Tomo-e PM is equipped with eight chips of the CMOS sensor arranged in a line along the RA direction, covering a sky area of 2.0 deg2. The maximum frame rate is 2 fps. The total data production rate is 80 MByte sec-1 at 2 fps, corresponding to approximately 3 TByte night-1. After laboratory testing, we have successfully obtained consecutive movie data at 2 fps with the Tomo-e PM in the first commissioning run conducted in the end of 2015.

The Tomo-e Gozen camera is a next-generation, extremely wide field optical camera, equipped with 84 CMOS sensors. The camera records about a 20 square degree area at 2 Hz, providing “astronomical movie data”. We have developed a prototype of the Tomo-e Gozen camera (hereafter, Tomo-e PM), to evaluate the basic design of the Tomo-e Gozen camera. Tomo-e PM, equipped with 8 CMOS sensors, can capture a 2 square degree area at up to 2 Hz. Each CMOS sensor has about 2.6 M pixels. The data rate of Tomo-e PM is about 80 MB/s, corresponding to about 280 GB/hour. We have developed an operating system and reduction softwares to handle such a large amount of data. Tomo-e PM was mounted on 1.0-m Schmidt Telescope in Kiso Observatory at the University of Tokyo. Experimental observations were carried out in the winter of 2015 and the spring of 2016. The observations and software implementation were successfully completed. The data reduction is now in execution.

We present the H$\alpha$ intensity map of the host galaxy of the repeating fast radio burst FRB 121102 at a redshift of z=0.193 obtained with the AO-assisted Kyoto 3DII optical integral-field unit mounted on the 8.2-m Subaru Telescope. We detected a compact H$\alpha$-emitting (i.e., star-forming) region in the galaxy, which has a much smaller angular size [$< 0".57$ (1.9 kpc) at full width at half maximum (FWHM)] than the extended stellar continuum emission region determined by the Gemini/GMOS z'-band image [$\simeq 1".4$ (4.6 kpc) at FWHM with ellipticity b/a=0.45]. The spatial offset between the centroid of the H$\alpha$ emission region and the position of the radio bursts is $0".08 \pm 0".02$ ($0.26 \pm 0.07$ kpc), indicating that FRB 121102 is located within the star-forming region. This close spatial association of FRB 121102 with the star-forming region is consistent with expectations from young pulsar/magnetar models for FRB 121102, and it also suggests that the observed H$\alpha$ emission region can make a major dispersion measure (DM) contribution to the host galaxy DM component of FRB 121102. Nevertheless, the largest possible value of the DM contribution from the H$\alpha$ emission region inferred from our observations still requires a significant amount of ionized baryons in intergalactic medium (the so-called `missing' baryons) as the DM source of FRB 121102, and we obtain a 90\% confidence level lower limit on the cosmic baryon density in the intergalactic medium in the low-redshift universe as $\Omega_{IGM} > 0.012$., Comment: 11 pages, 5 figures, and 1 table, accepted for publication in the Astrophysical Journal 2017 June 20

We compare the isophote shape parameter $a_{4}$ of early-type galaxies (ETGs) between $z\sim1$ and 0 as a proxy for dynamics to investigate the epoch at which the dynamical properties of ETGs are established, using cluster ETG samples with stellar masses of $\log(M_{*}/M_{\odot})\geq10.5$ which have spectroscopic redshifts. We have 130 ETGs from the Hubble Space Telescope Cluster Supernova Survey for $z\sim1$ and 355 ETGs from the Sloan Digital Sky Survey for $z\sim0$. We have developed an isophote shape analysis method which can be used for high-redshift galaxies and has been carefully compared with published results. We have applied the same method for both the $z\sim1$ and $0$ samples. We find similar dependence of the $a_{4}$ parameter on the mass and size at $z\sim1$ and 0; the main population of ETGs changes from disky to boxy at a critical stellar mass of $\log(M_{*}/M_{\odot})\sim11.5$ with the massive end dominated by boxy. The disky ETG fraction decreases with increasing stellar mass both at $z\sim1$ and $0$, and is consistent between these redshifts in all stellar mass bins when the Eddington bias is taken into account. Although uncertainties are large, the results suggest that the isophote shapes and probably dynamical properties of ETGs in massive clusters are already in place at $z>1$ and do not significantly evolve in $z, 22 pages, 21 figures. Accepted for publication in ApJ

LISS (Line Imager and Slit Spectrograph) is an imager and spectrograph equipped with a liquid crystal etalon and a low resolution grism. It is specialized to observe and map the emission and absorption lines of astronomical objects. A fully depleted and back illuminated 2K x 1K Hamamatsu CCD which has high sensitivity at redder wavelengths in optical bands enables this instrument to give a good performance in imaging and spectroscopic observations of emission lines such as [SIII]λλ 906.9/953.2 nm. We successfully carried out commissioning observations at the 1.6-m Pirka telescope of Hokkaido University in September/October 2012 and June/July 2013. In this paper, we describe the design and performance of LISS as well as its early observational results and future prospects.